The present invention relates to the field of energy absorption, in particular energy generated in connection with shock or impact forces, by means of passive devices being subjected to crushing or deformation, particularly for applications in the automotive field. The present invention relates more specifically to an energy absorber device in the form of a hollow conical or truncated body and a filling element comprising a plurality of such devices.
In numerous applications, it is necessary to provide safety means to absorb the energy resulting from a shock or impact. This is the situation in motor vehicles, particularly in the region of the doors so as to absorb the energy released during lateral shock resulting from impact to the side of said vehicle.
Various types of energy absorbers are already known and operate based on the principle of deformation under stress, typically between two surface elements, such as plates, layers or metal sheets. Thus, the use of one or more blocks of foam, of suitable density and rigidity, as an absorber element(s) is known. However, when the possible deformation distance is great (such as the vehicle's plates being separated by a large distance), the volume of foam needed to fill the void is equally great, producing an unacceptable and significant increase in cost and/or weight.
The use of hollow elongated bodies as energy absorbers is also known. These bodies are generally of plastic material or are plastically deformable, and are deformed by crushing under the action of pressure greater than a given intensity. The hollow bodies may, for example, be cylindrical or conical in shape and may be combined in a cellular structure or have the form of separate hollow bodies connected by a common base plate.
The energy absorption process of the known absorbers of this type is illustrated in a simplified manner in FIG. 1A, in the form of a force, or absorbed energy, curve versus on the displacement or the degree of crushing. The maximum permitted force (the force transmitted by the absorber during crushing) is generally set (by the constructor or by safety regulations) and the maximum permitted displacement is determined by the thickness available for filling or between the surface elements subject to impact, such as the inner and outer panels of a door.
In FIG. 1A, region A represents the energy potential that is not used by the absorber device, having been lost during crushing; region B represents the energy that is effectively absorbed by the device; and region C represents the energy released by the device (the rebound effect). The purpose of recent and current improvements is to reduce region A, with a view to absorbing a greater part of the energy when crushing begins following impact, to increase region B, and to control the intensity of the force transmitted (the plateau). However, known solutions that attempt to meet this objective do not comply with the ideal increase in resistance to crushing, depending on the degree of crushing, that is required. In fact, they all typically show an initial peak of resistance to significant deformation. This does not comply with the protection and safety arrangements being sought after since deformation only begins after a high level of intensity of the compression or pressure stress. This initial peak is seen in FIG. 1B.
An optimal energy absorption process, such as the one presently sought, should provide constant resistance to deformation during crushing (the stress plateau), or at the very least during a phase of significant initial deformation. Such a force curve diagram is seen in FIG. 3.
In an attempt to move towards the sought after optimal deformation process of FIG. 3, the production of hollow, conical stepped or tiered bodies, with preferred lines of rupture between steps, has been proposed (see for example EP-A-0 244 579, FR-A-2 797 669 and EP-A-0 673 072). This solution provides an energy absorption curve (force/displacement) (see FIG. 2) formed by a series of peaks, each corresponding to rupture in the region of one of the steps. This energy absorption curve, however, is not the ideal process that is being sought.
It has also been proposed to produce a hollow stepped body in which the steps have different resistances to crushing (see for example U.S. Pat. No. 3,998,485). This solution also gives an unsatisfactory energy absorption curve which is in the form of a series of peaks.
Another known solution proposes is an arrangement of hollow conical bodies of different heights or sizes (see for example FR-A-2 784 151). By distributing the initial peaks of resistance to deformation over a given crushing range, this allows a pseudo plateau of stress to be obtained, which is made up of adjacent peaks on a reference surface (comprising bodies of different sizes). However, such an arrangement still has undesirable peaks of stress in the locality of the crushing.
A further solution involves producing prior crushing or weakening of an aforementioned absorber device at the initial peak so as to eliminate a significant peak. This is represented by the broken line on FIG. 1B. However, this results in an additional manufacturing operation and a reduction in the overall energy that can be absorbed.
An energy absorber device, see FR-A-2 777 332, and consists of a hollow, generally cone-shaped body, the envelope of which is formed of at least two hollow stepped segments, of which the individual envelopes are of the same type of shape, are truncated or cylindrical, and are aligned with each other in an extension direction. The sections are of decreasing dimensions, at least on the outside, from an end segment forming the base step to the opposite end segment forming the top step of the body. The various truncated or cylindrical segments are connected to each other by an intermediate envelope portion or portions defining, with the aforementioned segments, tiers. The hollow body is suitable for being crushed into itself by return or reversal of the segment(s) of smaller section into the adjacent segment(s) of larger section, telescopically under the action of a pressure force, in the direction of alignment or extension, with an intensity greater than a predetermined value. The intermediate envelope portions respectively serve as initiation, return or reversal zones for the cylindrical segments of which they form the bases. The energy absorption process occurs with a plateau of relatively constant stress during crushing, this crushing occurring by reversal of the various steps. However, this device is not optimised in terms of the amount of energy absorbed per unit of height of the device, or in terms of resistance to buckling in the region of the recesses between successive steps (which may require the addition of supplementary reinforcement ribs, which may cause a peak of stress when crushing begins).
Accordingly, one object of the present invention is to overcome at least some of the limitations mentioned above, and in particular to improve upon the known energy absorber device.
In achieving the above, the present invention provides an energy absorber device characterised by a series of segments: a segment forming the base step having a height X and at least one other segment of smaller width having a height “h” corresponding to about, or preferably equal to, 2X.